1. Field of the Invention
The present invention relates to devices for in situ mixing to produce soil-cement columns. In particular, the present invention relates to a stabilizer for an auger that provides for straight accurate drilling of in situ soil-cement columns even in horizontal directions.
2. Description of Related Art
A method for soil solidification and stabilization is the construction of soil-cement columns. Soil-cement columns are conventionally constructed by mixing soil with a chemical hardener in situ. The need for excavating the soil, mixing the soil with the chemical hardener, and then replacing the mixed soil and hardener in the excavation site is advantageously avoided by using a one step process with special augers and shafts that mix soil and a chemical hardener while the soil remains under ground near its original position. Typically, the auger shaft performs the two functions: (1) rotating to drive the auger and to mix the soil, and (2) providing a path for injection of the chemical hardener during the mixing process. Conventional soil-cement column augers are disclosed in U.S. Pat. Nos. 4,9002,172 issued to Fukuda; 4,909,675 issued to Taki; 5,013,185 issued to Taki and Japanese patent Nos. 1197295 and 1197296.
One continuing problem in constructing soil-cement columns is the ability to form them in accurate inclined and horizontal directions. FIG. 1 illustrates a cross-sectional view of a hillside and a soil-cement column constructed in an inclined direction (perpendicular to the surface). The axis upon which the column was to be formed is shown by the dashed line. As can be seen, the auger is effected by gravity, and as the column is mixed and injected with cement the auger veers from its intended course downward. Similarly shown in FIG. 1B, the problem is more server when constructing a soil cement column in substantially horizontal direction. The column formed in FIG. 1B in nowhere near its intended path at the bottom of the column.
The prior art has attempted to resolve this problem by using rods with greater rigidity and strength to compensate for the forces of gravity and retain the auger on its intended path. To increase the strength off the drilling shaft, its size, in particular the diameter, must be increased. However, one problem with increasing the size of the shaft is there is less area for mixing blades and the efficiency in mixing the soil with a hardening agent decreases. Increasing the size of shaft also increases the volume of the column occupied by the drill which results in more exposed soil being produced. This is a significant problem because it adversely effects the strength of the column being constructed. The less the soil and hardening agent are mixed, the less the strength of the column. Thus, there a need for a system that will provide maximum mixing of soil and hardening agent, and allow columns to be constructed in the horizontal or inclined directions.